Mycorrhiza Research Research Articles

Rhizophagus irregularis, the model fungus in arbuscular mycorrhiza research, forms dimorphic spores.

Rhizophagus irregularis is the model species for arbuscular mycorrhizal fungi (AMF) research and the most widely propagated species for commercial plant biostimulants. Using asymbiotic and symbiotic cultivation systems initiated from single spores, advanced microscopy, Sanger sequencing of the glomalin gene, and PacBio sequencing of the partial 45S rRNA gene, we show that four strains of R. irregularis produce spores of two distinct morphotypes, one corresponding to the morphotype described in the R. irregularis protologue and the other having the phenotype of R. fasciculatus. The two spore morphs are easily distinguished by spore colour, thickness of the subtending hypha, thickness of the second wall layer, lamination of the innermost layer, and the dextrinoid reaction of the two outer spore wall layers to Melzer's reagent. The glomalin gene of the two spore morphs is identical and that of the PacBio sequences of the partial SSU-ITS-LSU region (2780 bp) obtained from single spores of the R. cf fasciculatus morphotype has a median pairwise similarity of 99.8% (SD = 0.005%) to the rDNA ribotypes of R. irregularis DAOM 197198. Based on these results, we conclude that the model AMF species R. irregularis is dimorphic, which has caused taxonomic confusion in culture collections and possibly in AMF research.

​Bibliometric Analysis of the Research Characteristics and Trends in Legume Mycorrhiza Field

Background: Legumes are notable for wide distribution and indispensable food function. Majority of legume species are known to form mycorrhizal symbioses. The visualized and quantitative analysis legume mycorrhiza research has been reported although much attention has been paid in this field. Methods: This study reviewed and analyzed systematically the research characteristics and trends in legume mycorrhiza by bibliometric method based on the citation data collected from the Web of Science Core Collection by CiteSpace software. Result: The publication concerning legume mycorrhiza research increases rapidly and is still a hotspot. The most active collaboration countries are USA, France, Germany, China and Australia, whereas the two institutions of University of Western Australia and Chinese Academy of Sciences collaborate most with others. The intellectual structure analysis showed that the main intellectual base is nitrogen-fixing of cereal. The top ranked of keyword by bursts was rhizobia with strength value of 5.2899, which began from 2016 and ended in 2018. The distinction of 24 bursting keywords is relatively small, which showed that the research hotpot and trend should be interaction between legume plants and mycorrhizal fungi for improving nutrition absorption, N-fixation, resistance to stress and their mechanisms in future.

Brief Overview of Arbuscular Mycorrhiza Research Conducted in Russia Over the XXTH Century

Arbuscular mycorrhiza (AM) is one of the most common terrestrial plant-microbe symbioses. The interest in studying AM is caused by its importance for the growth and nutrition of plants and its ecological role in preserving biological diversity. At present, 92% of plant families are known to form AM. Fungi in AM are obligate symbionts and belong to a monophyletic group – Glomeromycotina subdivision. Some researchers believe that formation of AM-symbiosis with fungi by ancient plants allowed them to inhabit land, which has led to the formation of the biosphere as we know it. AM is studied by researchers from around the world including Russia. This overview presents in brief the results of AM research in Russia during the Soviet period which did not receive international coverage due to its classified nature; the most prominent research schools and works of AM researchers are identified; main stages and lines of this research are listed, such as: distribution of AM in plant communities and different climatic zones, mycorrhiza anatomy and morphology, fungi species composition on different soils, collection of AM fungi and growing AM in vitro, physiological role of AM for agricultural plants, the impact different ecological factors have on AM fungi species composition and AM development, conditions for effective use of Am fungi to increase productivity and quality of agricultural plants as well as to perform biological recultivation of toxic soils and restore the fertility of degraded soils.

Life's rich tapestry : A tribute to Sally E. Smith (1941-2019).

With the recent passing away of Emeritus Professor Sally (Sarah) E. Smith, the mycorrhiza research community has lost one of its most outstanding members. Sally's contribution to knowledge in the fields of soil microbiology and root physiology will continue to be an inspiration to present and future scientists.

Growing Research Networks on Mycorrhizae for Mutual Benefits.

Research on mycorrhizal interactions has traditionally developed into separate disciplines addressing different organizational levels. This separation has led to an incomplete understanding of mycorrhizal functioning. Integration of mycorrhiza research at different scales is needed to understand the mechanisms underlying the context dependency of mycorrhizal associations, and to use mycorrhizae for solving environmental issues. Here, we provide a road map for the integration of mycorrhiza research into a unique framework that spans genes to ecosystems. Using two key topics, we identify parallels in mycorrhiza research at different organizational levels. Based on two current projects, we show how scientific integration creates synergies, and discuss future directions. Only by overcoming disciplinary boundaries, we will achieve a more comprehensive understanding of the functioning of mycorrhizal associations.

Professor Jos\xe9 Miguel Barea (1942\u20132018): a tribute to an inspiring scientist

The mycorrhiza and, more generally, soil microbiology research communities recently have lost one of their most ardent scientists. José Miguel Barea was a world leader of arbuscular mycorrhiza research and pioneered the establishment of such studies in Spain and Latin American. He was a prolific publisher, enthusiastic teacher of many graduate students and a genial host to visitors of his beloved Granada. He will be missed wherever mycorrhizasts gather.

Dr. Edward Hacskaylo: a memoir and tribute.

Edward Hacskaylo was a pioneer in many aspects of mycorrhiza research and significantly influenced our understanding of the physiology and ecology of mycorrhizas. This memoir highlights Dr. Hacskaylo's many contributions and his impact on mycorrhiza research, especially through his encouragement and mentoring of young scientists.

Cost-efficient production of in vitro Rhizophagus irregularis

One of the bottlenecks in mycorrhiza research is that arbuscular mycorrhizal fungi (AMF) have to be cultivated with host plant roots. Some AMF species, such as Rhizophagus irregularis, can be grown in vitro on dual-compartment plates, where fungal material can be harvested from a fungus-only compartment. Plant roots often grow into this fungus compartment, and regular root trimming is required if the fungal material needs to be free of traces of plant material. Trimming also increases unwanted contamination by other microorganisms. We compared 22 different culture types and conditions to a widely used dual-compartment culture system that we refer to as the “standard system.” We found two modified culture systems that allowed high spore production and low rates of contamination. We then compared the two modified culture systems with the standard system in more detail. In the two modified culture systems versus the standard system, a comparable number of spores were produced per plate, the necessity for root trimming was reduced, and there was significantly diminished contamination in the fungal compartment. A cost analysis showed that both modified culture systems were more economic than the standard culture system for the production of the same number of non-contaminated spores. The two modified culture systems provide an economic alternative for the production of contaminant-free fungal material which is ideal for studies requiring AMF DNA or RNA for genetics, genomics, and transcriptomic studies or for studies requiring relatively large amounts of fungal material for greenhouse experiments.

Highlights of the Seventh International Conference on Mycorrhiza in New Delhi—a conference to remember

The Seventh International Conference on Mycorrhiza (ICOM7) took place in New Delhi, India from January 6– 11, 2013. This was the first time that an ICOM had been held in Asia, and it was a clear success, with 356 registrants from 46 countries. Dr. Alok Adholeya headed a very active, helpful, and enthusiastic local organizing committee, comprising a large team from the Mycorrhiza Research Group at the Energy Research Instiute (TERI). Scientific presentations were given by 4 keynote speakers, 20 plenary speakers, 96 concurrent workshop presenters and 160 poster presenters. The official opening ceremony was one of the most remarkable parts of ICOM7. The audience was spellbound, and even emotional from some reports, as they listened to the Indian Minister for Science and Technology, Mr. S. Jaipal Reddy, describe how important mycorrhiza research is to India. Many people were impressed to hear that Minister Reddy had spent the previous day at TERI learning about the mycorrhiza research going on there. Many of us were thinking: “That would ne]ver happen in my country!”. In a stimulating opening keynote presentation, Francis Martin described insights from the Mycorrhiza Genome Initiative Consortium. Using bioinformatics to compare the genomes and transcriptomes of ectomycorrhizal and wood-decay fungi, this group is identifying key steps in the evolution of ectomycorrhizal symbiosis. The rest of the opening plenary session on “Developmental, Functional and Environmental Genomics of Mycorrhiza” was equally stimulating. Anders Tunlid presented several types of evidence that Paxillus involutus degrades soil organic matter primarily using radical-based degradation systems, rather than the lignin and Mn-peroxidases seen in white-rot fungi, and that N, not C, is absorbed from the breakdown products. Natalia Requena described putative hexose transporters expressed in arbuscules and intraradical hyphae, which could be responsible for transfer of host C into the fungus. Tuesday’s plenary session focused on “Physiology, including Carbon and Nutrient Exchange between Symbionts and the Saprotrophic/Biotrophic Continuum”. Keynote speaker Uwe Nehls described recent findings on sugar, ammonium, and nitrate transporters that are bringing us closer to understanding the molecular basis for the transfer of nutrients between symbionts. In particular, the old paradigm of sugar being exported from root cells as sucrose and being broken down in the apoplast by plant-derived invertase before being taken up by fungal cells is being challenged by new data. Nutrient transfer in common mycelial networks was a hot topic at the conference: in some cases, but not others, hosts and arbuscular mycorrhizal fungi (AMF) exchange C and P in a “tit-for-tat” manner, with the rate of transfer of C influenced by the nutrient status of the host. While community ecology of mycorrhizal fungi is always well represented at ICOMs, the plenary session on “Population, Community and Physiological Ecology” and other related workshops at ICOM7 showcased everincreasing and ever-evolving fungal community studies. Keynote speaker, Ian Dickie, took us through ecosystem processes that may occur during the transition between AMand ectomycorrhizal (EM)-dominated ecosystems to M. D. Jones (*) International Mycorrhiza Society, Biology Department, University of British Columbia (Okanagan Campus), Sci 385, 3333 University Way, Kelowna, BC V1V 1V7, Canada e-mail: melanie.jones@ubc.ca

Resolving uncertainty in the carbon economy of mycorrhizal fungi

Resolving uncertainty in the carbon economy of mycorrhizal fungi

Plant–fungal symbiosis en gros and en détail

Plant–fungal symbiosis <i>en gros</i> and <i>en détail</i>

The Ringing Rocks Foundation

Research on mycorrhizal interactions has traditionally developed into separate disciplines addressing different organizational levels. This separation has led to an incomplete understanding of mycorrhizal functioning. Integration of mycorrhiza research at different scales is needed to understand the mechanisms underlying the context dependency of mycorrhizal associations, and to use mycorrhizae for solving environmental issues. Here, we provide a road map for the integration of mycorrhiza research into a unique framework that spans genes to ecosystems. Using two key topics, we identify parallels in mycorrhiza research at different organizational levels. Based on two current projects, we show how scientific integration creates synergies, and discuss future directions. Only by overcoming disciplinary boundaries, we will achieve a more comprehensive understanding of the functioning of mycorrhizal associations.

Mycorrhizas and nutrient cycling in ecosystems - a journey towards relevance?

Progress towards understanding the extent to which mycorrhizal fungi are involved in the mobilization of nitrogen (N) and phosphorus (P) from natural substrates is reviewed here. While mycorrhiza research has emphasized the role of the symbiosis in facilitation of capture of these nutrients in ionic form, attention has shifted since the mid-1980s to analysing the mycorrhizal fungal abilities to release N and P from the detrital materials of microbial faunal and plant origins, which are the primary sources of these elements in terrestrial ecosystems. Ericoid, and some ectomycorrhizal fungi have the potential to be directly involved in attack both on structural polymers, which may render nutrients inaccessible, and in mobilization of N and P from the organic polymers in which they are sequestered. The advantages to the plant of achieving intervention in the microbial mobilization-immobilization cycles are stressed. While the new approaches may initially lack the precision achieved in studies of readily characterized ionic forms of N and P, they do provide insights of greater ecological relevance. The results support the hypothesis that selection has favoured ericoid and ectomycorrhizal systems with well developed saprotrophic capabilities in those ecosystems characterized by retention of N and P as organic complexes in the soil. The need for further investigation of the abilities of arbuscular mycorrhizal fungi to intervene in nutrient mobilization processes is stressed.

Reproductive significance of feeding on saprobic and arbuscular mycorrhizal fungi by the collembolan, Folsomia candida

1. Collembolans have often been credited with negatively affecting arbuscular mycorrhizal (AM) symbioses, mainly by grazing and severing the associated external fungal network from host roots. However, most previous experiments were performed using relatively ‘clean’ systems where other, non‐mycorrhizal, fungi were largely excluded. Yet, plant rhizospheres harbour a wide variety of highly palatable non‐AM fungi, most of which have saprobic lifestyles. 2. In this study we isolated and cultured several rhizosphere fungi, and the collembolan, Folsomia candida, from the Long‐Term Mycorrhiza Research Site, University of Guelph, Canada, to test the hypothesis that, given a choice, collembolans would prefer to feed on saprobic fungi and that such a choice is of adaptive significance to the animals. 3. A laboratory food preference experiment revealed that F. candida favours common saprobic fungi over a variety of AM fungi. Coincidentally, fecundity levels across two Folsomia generations were higher when animals fed exclusively on the preferred fungus, Alternaria alternata. When fed less palatable fungi, fecundity was greatly reduced; in fact animals from the F1 generation were unable to produce any eggs when placed on an exclusive diet of one of the following three AM fungi, Acaulospora spinosa, Scutellospora calospora and Gigaspora gigantea. 4. These results indicate that a strict diet of AM fungi by collembolans has reproductive consequences. Therefore, we propose that under natural conditions these animals spend more time feeding on common saprobic fungi rather than their AM counterparts. This suggests that previous ‘clean’ studies that investigated the interactions between collembolans and AM fungi may have reported exaggerated effects of animal grazing. The influence of collembolans on the functioning of AM symbioses, under more natural conditions, remains not well understood.

ICOM2 shows that mycorrhiza research is strong!

ICOM2 shows that mycorrhiza research is strong!

Tansley Review No. 76 Helper bacteria: a new dimension to the mycorrhizal symbiosis.

The symbiotic establishment of mycorrhizal fungi on plant roots is affected in various ways by the other microorganisms of the rhizosphere, and more especially by bacteria. This review discusses the case of some of these bacteria which consistently promote mycorrhizal development, leading to the concept of 'mycorrhization' helper bacteria (MHBs). Examples of MHB evidence are given from the literature, with special reference to the Douglas fir (Pseudotsuga menzeisii Mirb. Franco) Laccaria laccata Scop, ex Fr. ectomycorrhizal combination which has been more extensively studied. The fungal specificity of some MHBs and the various mechanisms underlying their effect are discussed, considering five hypotheses: effects on the receptivity of the root, effects on the root-fungus recognition, effects on the fungal growth, modification of the rhizospheric soil, and effects on the germination of the fungal propagule. MHBs are then considered for their ecological and evolutionary implications, and examples of practical applications in forest nurseries are given: when added to the fungal inoculum, MHBs can improve the success of ectomycorrhizal inoculation of planting stocks with fungi selected for their outstanding growth stimulation after outplanting. The conclusion points out a number of fundamental questions which remain unanswered about mycorrhization helper bacteria and suggests some investigation priorities in this new field of mycorrhiza research. Contents Summary 197 I. Introduction 197 II. Evidence for helper bacteria 198 III. Fungus-specificity of MHBs 200 IV. Mechanisms underlying the MHB effect 201 V. Ecological and evolutionary implications of MHBs 205 VI. Practical applications of MHBs 206 VII. Conclusions and perspectives 208 Acknowledgements 208 References 208.

Appropriate controls for vesicular–arbuscular mycorrhiza research

SUMMARYSunflower (Helianthus animus L.) and mustard (Brassica hirta Moench.) plants were grown in autoclaved soil to which was added various components of soil inoculum. Use of inocula containing mycorrhizal propagules ultimately resulted in growth promotions which were related to improved phosphorus nutrition. Inoculation with soil containing mycorrhizal propagules caused an initial growth depression in comparison with plants receiving no inoculation, but inoculation with washed spores did not. For several reasons, the growth depression caused by inoculation with soil was not attributable to mycorrhizal infection. First, the growth depression was evident before mycorrhizal infections had become established. Second, the growth depression was also evident when either soil or soil sievings, both lacking mycorrhizal propagules, were used. Third, similar growth depressions were observed in mustard. The results suggest that careful selection of appropriate controls for mycorrhizal plants must be made, particularly if the emphasis is on early phases of plant growth. Use of non‐sterile soil reduced the extent of mycorrhizal infection.

Buchbesprechungen / Book Reviews

Book reviewed in this articles: Müller, E., und W. Loeffler, Mykologie. Ayres, P. G., Effects of disease on the physiology of the growing plant. Staples, R. C, and G. H. Toenniessen (Eds.), Plant Disease Control: Resistance and Susceptibility. Schenck, N. C. (Ed.), Methods and Principles of Mycorrhiza Research. Dekker, J., and S. G. Georgopoulos (Eds.), Fungicide resistance in crop pro‐tection. Perkow, W., Wirksubstanzen der Pflanzen‐ und Schadlingsbekampfungsmittel.